In recent years, an imaging device (hereunder may also be referred to as an “OCT device”) using optical coherence tomography (OCT) making use of coherence of low coherence light has been put into practical use. Since it is possible to obtain a tomographic image at a resolution of an order of a wavelength of light that is incident upon a sample, the tomographic image of the sample can be obtained with high resolution.
In particular, in obtaining a tomographic image of a fundus/retina in the ophthalmologic field, the OCT device is becoming an indispensible device. Even outside the ophthalmologic field, tomographic observation of the skin and tomographic imaging operation of a wall of a circulatory organ or a digestive organ using the OCT device as an endoscope or a catheter are carded out.
Here, two types of OCT method are primarily available, that is, time domain-OCT (TD-OCT) and Fourier domain-OCT (FD-OCT). The FD-OCT is a method in which spectrum information of interference light is subjected to Fourier transformation, to obtain together pieces of intensity information corresponding to depth-direction positions. Therefore, the FD-OCT can obtain a tomographic image at a higher speed than the TD-OCT in which a coherence gate position is changed for obtaining a depth-direction position.
In the OCT device, when making measurements at a high resolution, a measurement area per beam becomes narrow, as a result of which a relatively large amount of measurement time is required. In particular, when the OCT device is used in ophthalmology, imaging operations are required to be performed at high speeds. This is because images may be displaced from each other by, for example, involuntary eye movement during the imaging operation.
PCT Japanese Translation Patent Publication No. 2008-508068 (Patent Literature 1) discusses a method that uses a plurality of beams and that narrows a measurement area per one beam to reduce the measurement time.
In the Patent Literature 1, an interferometer that separates nine beams into measuring lights and reference lights is used. Interference lights obtained from the respective beams are dispersed, and the dispersed interference lights are detected same two-dimensional sensor array for the plurality of beams.